Variable phase shifter



April 3, 1951 w. c. MORRISON VARIABLE PHASE SHIFTER Filed June 13, 1946 LAAAZAAA 'vvIvIvI mmvroge. Wendell 61111012 18017 (LE 1 1 A 7' TOP/V5 Y Patented Apr. 3, 1951 VARIABLE PHASE SHIFTER Wendell C. Morrison, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 13, 1946, Serial No. 676,549

3 Claims.

This invention relates to phase shifting devices such as are adapted to vary the phase relation between an applied alternating potential input and a delivered alternating potential output or to phase modulate an output signal.

Many difierent types of devices have been provided or proposed for controlling and changing the phase relation between an input potential and an output potential. Such devices have involved control elements which are more or less complicated depending on the type of device involved. Insofar as is known none of these control elements have been such as to involve nothing more than variation of the bias potential applied to an electron discharge device. This result is achieved by the present invention.

In accordance with the present invention, this result is produced by means of an electron discharge device of the heptode or pentagrid converter type. Such a device includes a cathode, an anode, a first control grid, at second control grid, a screen or shield grid which functions to shield the second control grid from the other electrodes of the device, and a suppressor grid which functions to retard the flight of secondary electrons and reflect them back to the anode. Such an electron discharge device is normally used to perform the functions or" an oscillator, a mixer, and an amplifier. The present invention involves certain modifications in its input and output connections whereby it may be made to shift the phase of its output potential through an angle of 180 degrees with respect to its input potential or to phase modulate a carrier wave.

Thus (1) the input potential superimposed on a unidirectional bias potential of relatively small value is applied to the first control grid, 2) the second control grid has applied to it either a modulating frequency with suitable bias or a unidirectional bias potential which is varied from zero to a predetermined negative value, and (3) positive potential is applied through separate resistors to the anode and screen grid. When the second control grid has applied to it only such variable bias potential, it functions to shift the output current from the electron discharge device so that the input and output potentials (1) are in phase when the bias potential is zero, and (2) are 180 degrees out of phase when the bias potential has its maximum negative value.

By connecting a capacitor between the cathode and screen grid of the heptode, there is produced in its anode or output circuit a potential which may be varied in phase over a range approaching 180 degrees as a limit.

When a modulating frequency is superimposed on the unidirectional bias potential of its second grid, the heptode functions as a phase modulator.

Important objects of the invention are to provide an improved phase shifting device, to provide an improved phase modulator, and to provide a type of circuit whereby the usefulness of the type of electron discharge device under consideration is extended into new fields.

The invention will be better understood from the following description considered in connection with the accompanying drawings and its scope is indicated by the appended claims.

Referring to the drawings:

Figure 1 is a wiring diagram of a phase shifting device which functions to produce an output potential which is of variable amplitude and is either in phase or out of phase with its input potential,

Figure 2 is a wiring diagram of a device which operates to gradually vary the phase relation between its input and output potentials, and

Figure 3 illustrates the device of Figure 2 as modified to operate as a phase modulator.

The device of Figure 1 includes a heptode l0 (6SA7 for example) which has a cathode I I, a first control grid [2, a screen grid I 3, a second control grid I4, a suppressor grid l5 and an anode I6.

A unidirectional operating voltage for the tube Ill is applied to the anode l6 and the screen grid is from a source (not shown) through a terminal designated +250 v., and through a 10,000 ohm resistor l6 and a 15,000 ohm resistor l7, respectively. The suppressor grid i5 is connected to the cathode H which is grounded. Bias potential is applied to the first control grid 12 from a 4.5 v. source 18 through a resistor l9. This resistor 19 is connected in series with the secondary winding 20 of a transformer having a primary winding 2| to which an alternating potential may be applied through the input terminals 22-23' of the phase shifting device. Potential for controlling the phase relation between the alternating potential applied to the terminals 2223 and that delivered through a capacitor 24 to the output terminals 25-28 is applied to the second control grid 14 from a resistor 21 which is connected in paralle1 with a 7.5 v. source 28 and is grounded (hence, connected to the cathode l I) at it most positive terminal.

It is apparent that the voltage applied to the first control grid 12 includes a unidirectional component derived from the source l8 and. an alternating component derived from the second- 3 ary winding 20 and that the value of the alternating component Es may be adjusted by a movable contact 29 of the resistor I9. The phase shifting control Voltage E likewise may be varied in value by moving the contact 30 of the resistor 21.

While the theory of operation of the phase shifting device of Figure l is somewhat uncertain, it is now believed that the tube Hi acts as an amplifier when the control voltage Ec is near zero. Under this condition, the alternating voltage developed across the resistor I6 .is 180 .out of phase with the input signal Es. The voltage developed across the resistor I? is in phase with that across the resistor 16 and produces degeneration for the reason that the screen grid I3 lies in the electron stream. Thus the resistor IT has a relatively large signal voltage across it which is 180 out of phase with the voltage E and is applied to that part of the grid I3 which lies between the grids I4 and I5.

,As the control voltage Ec is made more negative, more electrons travel to that part of the grid I3 which lies between the grids I2 and I I (lowering the screen grid voltage) and fewer electrons travelto the anode I6 (raising the anode voltage). At some particular value of E0, the modulation of the cathode-to-anode electron stream by the signal E5 on the grid I2 is equal to the modulation by the signal on that part of the grid I3 between the grids It and I5. Since these two grid signals are 180 out of phase with one another, the net result is no signal in the anode circuit.

As Ec is further increased in a negative direction, the signal on screengrid I3 continues to increase and the voltage of the anode I6 continues to rise. The result might be considered as a virtual cathode existing between the grid i l and the part of the grid I3 between the grids I4 and I5, which is partially modulated by the signal on grid I2 but is modulated much more by the large signal on the part of grid I3 between the grids M and I5. The resulting signal across the resistor i8 is 180 out of phase with the signal on the upper part of the grid I3 and the anode voltage now is in phase with E5.

If Es has a value of about 0.05 volt r. m. s. and EC is varied from zero to -6 volts, the output voltage between the terminals and 26 is shifted 180 degrees. This output voltage has a value of about three volts peak-to-peak when the terminal 30 isconnected to the grounded side of the resistor El. As the terminal 3! is made more negative, the output voltage decreases in value to approximately zero and then increases to a value of about three volts peak-to-peak.

The phase shifter of Figure 2 differs from that of Figure 1 in'that (l) a capacitor SI is connected between the screen grid I3 and cathode II of the device I0, and (2) bias voltage is applied to the grids I2 and I4 from a common battery and resistor 32. The provision of the capacitor 3i makes it possible to shift the phase of the output voltage E0 gradually over a phase angle which approaches 180.

As previously indicated the alternating voltage on the anode i6 is the resultant of two separate modulations of the cathode-to-anode electron stream. Thus the signal Es on the grid I2 of Figure 2 modulates the electrons emitted from the cathode II. This not only produces a signal in the anode circuit but also a signal in the circuit of the screen grid I3. The signal on the grid I3 is shifted in phase from the signal on the 4 anode I6 by the capacitor 3! in conjunction with the screen grid-to-cathode impedance.

When the control voltage E6 is near zero, the anode voltage E0 is approximately 180 out of phase with the voltage Es- The discrepancy is caused by a small amount of modulation introduced by the out-of-phase signal on the screen grid I3. As the control voltage E0 is made more negative, more electrons go to the grid I3 thus increasing the amplitude of the signal on both parts of the grid I3. Thus the anode signal is modulated more and more by the screen grid signal as E0 is made more negative. By a suitable choice of the capacitor 3I, the phase of the screen grid signal .may be made so that the phase shift of the output voltage E0 approaches 180 as a limit. realized at the expense of constant output amplitude. It has been found that a phase shift range of about may be obtained with an amplitude variation of about 6 db.

Figure 3 shows the circuit as rearranged to function as a phase modulator. Thus the resistor I6 of Figures 1 and 2 is replaced by an anode load impedance 33, a modulating frequency i2 is applied to the grid I4 through a transformer 34. and bias potential is applied to the grid I4 from a source shown as a battery 35.

A carrier wave fl is applied to the grid I2 through the transformer 20-2I and bias potential is applied to this grid from a source I8. The output voltage E0 in this case is a wave which has its phase modulate-d in accordance with the amplitude of the modulating frequency f2.

The invention thus provides a simple and reliable phase shifting or phase modulating device which is'of relatively light construction, involves only a single electron discharge device and is readily operated by the variation of a single control grid potential.

I claim as my invention:

1;. The combination of an electron discharge device including a cathode and anode, a screen grid and first and second control grids, a terminal adapted to be connected to a unidirectional voltage source, an impedance connected between said terminal and said anode, a resistor connected between said terminal and said screen grid, a capacitor connected between said screen grid and said cathode, and a circuit connecting said second control grid to said cathode, said circuit comprising (1) a unidirectional voltage source having a positive terminal connected to said cathode, and (2) a resistor connected in parallel with said voltage source and having'a movable contact connected to said second control grid.

2. An alternating voltage phase shifter comprising an electron discharge device including a cathode and anode, a screen grid and first and second control grids, a terminal adapted to be connected to a unidirectional voltage source, a first resistor connected between said terminal and said anode, a second resistor connected between said terminal and said screen grid, a capacitor connected between said screen grid and said cathode, means for applying an alternating input potential to said first control grid, and a circuit connecting said second control grid to said cathode, said circuit comprising a variable unidirectional voltage source.

3. The combination of an electron discharge device including a cathode and anode, a screen grid and first and second control grids, a terminal adapted to be connected to a unidirec- Increased limit of phase shift is 5 6 tional voltage source, a load impedance connected REFERENCES CITED between a anode sald, termmal' 5 The following references are of record in the passed resistor connecting said screen grld to said file of this patent: terminal, a capacitor connected from said cathode to the junction point of said resistor and 5 UNITED STATES PATENTS said screen grid, means for applying an alternat- Number Na D t ing input potential to said first cont-r01 grid, and 2,085,739 Crosby July 6, 1937 means for applying to said second control grid a 2,159,238 Usselman May 23, 1939 variable magnitude negative unidirectional po- 2,194,532 Usselman Mar. 26, 1940 tential to vary the phase relation between the 10 2,238,249 Crosby Apr. 15, 1941 voltages at said first cont-r01 grid and said anode. 2,321,269 Artzt June 8, 1943 WENDELL C. MORRISON. 2,380,947 Crosby Aug. 7, 1945 

